Honeycomb structural body and method for manufacturing the same

ABSTRACT

A honeycomb structural body  40  includes: a partition wall  48  formed of a porous ceramic which forms and defines a plurality of cells  47  each functioning as a flow path of a fluid and extending from one end surface to the other end surface; and an outer circumference wall  49  formed along the outermost circumference, where an oxide ceramic containing a Fe 3 O 4  phase in which a solute component capable of forming a spinel-type oxide with Fe is solid-dissolved is formed.

The present application claims priority from U.S. provisionalapplication No. 62/059,209 filed on Oct. 3, 2014, and U.S. provisionalapplication No. 62/075,397 filed on Nov. 5, 2015, the entire contents ofboth of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a honeycomb structural body and amethod for manufacturing the same.

2. Description of the Related Art

Hitherto, as a joined body, a joined body in which a pair of electrodeseach formed of a metal layer is provided on a surface of a honeycombbody formed of a porous ceramic has been proposed (for example, seePatent Literature 1). According to this joined body, the metal layercontains Cr and/or Fe, a diffusion layer formed of a metal silicide ispresent at a boundary portion with the honeycomb body, and thereliability of the electrical connection is ensured in ahigh-temperature environment. In addition, as the joined body, a joinedbody has been proposed in which pores of a porous ceramic are filledwith a ceramic, and a metal component is joined to the porous ceramicwith an active metal-containing solder material interposed therebetween(for example, see Patent Literature 2). In this joined body, the porousceramic and the metal component are joined to each other using a Ag—Cueutectic crystal. Furthermore, as the joined body, a joined body inwhich a ceramic member formed of a silicon nitride sintered body and ametal member are joined to each other with a buffer layer interposedtherebetween has been proposed (for example, see Patent Literature 3).In this joined body, the buffer layer is configured so that a siliconnitride sintered body layer containing 5 to 20 percent by mass of anitride of an active metal, a low-Young's modulus metal layer formed ofa transition metal and an alloy thereof, and a silicon nitride sinteredbody layer containing 25 to 70 percent by mass of a nitride of an activemetal are sequentially arranged.

As a honeycomb structural body, an exhaust gas cleaning apparatus hasbeen proposed in which the thickness of a partition wall of acylindrical carrier is set so that electrical resistances of all currentpaths between terminals are equal to each other, and the cylindricalcarrier is heated by supplying electricity thereto through electrodes toincrease the temperature of a catalyst supported by the carrier to itsactive temperature (for example, see Patent Literature 4). It has beendisclosed that according to this structural body, the carrier isuniformly heated, and even at cold start of an engine, the catalystsupported by the carrier can be heated to the active temperature. Inaddition, as the honeycomb structural body, a honeycomb structural bodyhas been proposed in which from a composite material containing MoSi₂and at least one type of Si and SiC, electrode films, electrodeterminals, and a substrate are manufactured (for example, see PatentLiterature 5). It has been disclosed that this structural body can beconfigured to have a low volume resistivity and a low temperaturedependence thereof as compared to those of SiC, SiC—Si, or the like.Furthermore, as the honeycomb structural body, a honeycomb structuralbody has been proposed in which a pair of electrode portions is formedso that each electrode portion has a belt shape extending in a cellformation direction (for example, see Patent Literature 6). It has beenproposed that in this structural body, the electrode is formed using SiCor Si.

CITATION LIST Patent Literature

[Patent Literature 1] JP 2011-246340 A

[Patent Literature 2] JP 2001-220252 A

[Patent Literature 3] JP 6-1670 A

[Patent Literature 4] JP 2011-99405 A

[Patent Literature 5] JP 2014-62476 A

[Patent Literature 6] WO 2011/125815 A1

SUMMARY OF THE INVENTION

However, since a joining layer of each of the joined bodies disclosed inPatent Literatures 1 to 3 is formed of a metal, there have beenproblems, such as a low heat resistance, a low oxidation resistance, anda low joining reliability.

In the honeycomb structural bodies disclosed in Patent Literatures 4 to6, although Cu, Al, Si, and/or the like is used as an electrodematerial, the heat resistance and the oxidation resistance are still notsufficient. In Patent Literature 5, although MoSi₂ is used, Mo may beselectively oxidized at 300° C. to 600° C. in some cases, and the heatresistance and the oxidation resistance are still not sufficient.Accordingly, the electrically conductive properties may be degraded,and/or the heat generation distribution may become uneven in some cases.

The present invention was made in consideration of the problemsdescribed above, and a primary object of the present invention is toprovide a joined body in which two members can be more easily and morereliably joined to each other and a method for manufacturing the joinedbody.

Another primary object of the present invention is to provide ahoneycomb structural body which can further increase the electricallyconductive properties and a method for manufacturing the same.

Through intensive research carried out to achieve the above primaryobjects, the present inventors found that when a predetermined componentis solid-dissolved in a Fe-containing oxide, two members can be moreeasily and more reliably joined to each other, and the electricallyconductive properties can be further improved, and as a result, thepresent invention was made.

The present invention provides a joined body comprising:

a first member;

a second member; and

a joint portion which is formed of an oxide ceramic containing a Fe₃O₄phase in which a solute component capable of forming a spinel-type oxidewith Fe is solid-dissolved and which joins the first member and thesecond member.

The present invention also provides a method for manufacturing a joinedbody in which a first member and a second member is joined to eachother, the method comprising:

a step of forming a laminate in which between the first member and thesecond member, a joint layer including a Fe metal powder and a solutecomponent powder which contains a solute component capable of forming aspinel-type oxide with Fe; and a joining step of firing the laminate ina temperature range lower than the melting point of a Fe oxide to forman oxide ceramic functioning as a joint portion which joins the firstmember and the second member.

The present invention provides a honeycomb structural body comprising: apartition wall formed of a porous ceramic which forms and defines aplurality of cells each functioning as a flow path of a fluid andextending from one end surface to the other end surface; and an outercircumference wall formed along the outermost circumference,

wherein an oxide ceramic containing a Fe₃O₄ phase in which a solutecomponent capable of forming a spinel-type oxide with Fe issolid-dissolved is formed.

The present invention also provides a honeycomb structural bodycomprising: a partition wall formed of a porous ceramic which forms anddefines a plurality of cells each functioning as a flow path of a fluidand extending from one end surface to the other end surface; and anouter circumference wall formed along the outermost circumference,

wherein an electrode formed of an oxide ceramic containing a Fe₃O₄ phasein which a solute component capable of forming a spinel-type oxide withFe is solid-dissolved is formed on an outer surface of the honeycombstructural body so that the ratio of a length L1 of the electrode to atotal length L of the honeycomb structural body in the flow pathdirection is in a range of 0.1 to 1 and the ratio of a length X1 of theelectrode to an outer circumference length X of the surface of thehoneycomb structural body perpendicular to the flow path is in a rangeof 0.02 to 0.3.

The present invention further provides a method for manufacturing ahoneycomb structural body comprising: a partition wall formed of aporous ceramic which forms and defines a plurality of cells eachfunctioning as a flow path of a fluid and extending from one end surfaceto the other end surface; and an outer circumference wall formed alongthe outermost circumference, the method comprising:

a forming step of, by using a raw material powder including a Fe rawmaterial powder which contains at least one of a Fe metal powder and aFe oxide powder and a solute component powder which contains a solutecomponent capable of forming a spinel-type oxide with Fe, forming anoxide ceramic layer containing a Fe₃O₄ phase in which the solutecomponent is solid-dissolved for the honeycomb structural body.

According to the joined body and the method for manufacturing the sameof the present invention, the first member and the second member arejoined with the oxide ceramic containing a Fe₃O₄ phase in which a solutecomponent capable of forming a spinel-type oxide with Fe issolid-dissolved. This oxide ceramic is made more thermally stable by thesolute component. Therefore, the two members can be more reliablyjoined. in the method for manufacturing a joined body, a joint layerincluding a Fe metal powder and a solute component powder which containsa solute component capable of forming a spinel-type oxide with Fe isformed and fired, and thus the two members can be more easily joined.

According to the honeycomb structural body and the method formanufacturing the same of the present invention, the oxide ceramiccontaining a Fe₃O₄ phase in which a solute component capable of forminga spinel-type oxide with Fe is solid-dissolved is formed. This oxideceramic is made more thermally stable by the solute component.Therefore, degradation of the electrically conductive properties can bemore reliably prevented. In the method for manufacturing a honeycombstructural body, the raw material powder can be sprayed, and thus theFe₃O₄ phase that is stable at high temperature can be easily formed andthe oxide ceramic containing the Fe₃O₄ phase can be easily formed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view showing one example of a schematicstructure of a joined body 20.

FIG. 2 is an explanatory view of an intrusion depth of an oxide ceramicinto a porous ceramic.

FIG. 3 is an explanatory view of a honeycomb structural body 40 which isone example of the joined body 20.

FIG. 4 is an explanatory view of an electrode portion 45B.

FIG. 5 is an explanatory view of a honeycomb structural body 40B.

FIGS. 6A-6B show explanatory views of a total length L, a length L1, anouter circumference length X, and a length X1 of the honeycombstructural body.

FIG. 7 is an explanatory view of a honeycomb structural body 40C whichis one example of a joined body 20C.

FIG. 8 shows x-ray diffraction measurement results of ExperimentalExamples 2 and 3.

FIG. 9 is an explanatory view of a joined body 60 for mechanicalstrength measurement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, embodiments of the present invention will be described withreference to the drawings. FIG. 1 is an explanatory view showing oneexample of a schematic structure of a joined body 20 according to oneembodiment of the present invention. FIG. 2 is an explanatory view of anintrusion depth of an oxide ceramic into a porous ceramic. FIG. 3 is anexplanatory view of a honeycomb structural body 40 which is one exampleof the joined body 20. FIG. 4 is an explanatory view of an electrodeportion 45B.

The joined body 20 includes a first member 21, a second member 22, and ajoint portion 30 which is formed of an oxide ceramic (hereinafter simplyreferred to as an oxide ceramic in some cases) containing a Fe₃O₄ phasein which a solute component capable of forming a spinel-type oxide withFe is solid-dissolved and which joins the first member 21 and the secondmember 22.

The first member 21 and the second member 22, each of which is an objectto be joined, may be either a porous ceramic or a dense material. Thefirst member 21 and the second member 22 each may be either a memberhaving electrically conductive properties or a member having noelectrically conductive properties. Since a Fe₃O₄ phase has relativelyhigh electrically conductive properties among metal oxides, it ispreferable that the first member 21 and the second member 22 each haveelectrically conductive properties and that the joined body 20 haselectrically conductive properties. Incidentally, the term “havingelectrically conductive properties” indicates the case in which theelectrical conductivity is 10 S/cm or more, and the term “having noelectrically conductive properties” indicates the case in which theelectrical conductivity is less than 10⁻⁶ S/cm.

The porous ceramic is not particularly limited as long as having aporous property. As a ceramic having a porous property, any ceramic maybe used as long as having open pores in its surface. For example,although a ceramic having a porosity of 10 percent by volume or more maybe used, the porosity is preferably 20 percent by volume or more andmore preferably 40 percent by volume or more. In view of easy formation,the porosity is preferably 90 percent by volume or less. The porosity ofthe porous ceramic may be appropriately selected in accordance with theapplication. The average pore diameter of this porous ceramic ispreferably, for example, in a range of 1 to 300 μm. When the averagepore diameter is in the range described above, an oxide ceramic islikely to intrude into pores of the porous ceramic and may be moretightly joined thereto. This average pore diameter is more preferably 5μm or more and further preferably 10 μm or more. This average porediameter is more preferably 100 μm or less and further preferably 50 μmor less. The porosity and the average pore diameter of the porousceramic described above each indicate the measurement result obtained bya mercury intrusion method.

The porous ceramic may be formed so as to contain at least one inorganicmaterial selected, for example, from a carbide, such as silicon carbide,titanium carbide, zirconium carbide, or a boron carbide; a nitride, suchas silicon nitride, aluminum nitride, titanium nitride, or zirconiumnitride; an oxynitride such as sialon; a silicide such as molybdenumsilicide; and zirconium phosphate. The porous ceramic may be formed soas to contain at least one inorganic material selected, for example,from cordierite, mullite, zeolite, aluminum titanate, aluminum oxide,zirconium oxide, titanium oxide, silicon oxide, and magnesium oxide. Theshape of the porous ceramic is not particularly limited and may beselected in accordance with the application, and may be, for example, aplate shape, a cylindrical shape, and a honeycomb shape, and thestructure through which a fluid is allowed to pass. In particular, thisporous ceramic may be a honeycomb structural body having a partitionwall portion which forms a plurality of cells each functioning as a flowpath of a fluid.

The joint portion 30 may be an oxide ceramic which intrudes into pores23 of the porous ceramic and which joins this porous ceramic to anothermember. A depth (intrusion depth) of intrusion of this oxide ceramicinto the pores of the porous ceramic is preferably 10 μm or more. Thereason for this is that the joining strength can be further increased.This intrusion depth is more preferably 15 μm or more and furtherpreferably 20 μm or more. This intrusion depth is preferably in a rangeof 50 μm or less. A measurement method of this intrusion depth will bedescribed. As shown in FIG. 2, a cross-section in which the first member21 of the porous ceramic, the second member 22, and the joint portion 30(oxide ceramic) can be simultaneously observed is mirror-polished. Thispolished surface is observed using a scanning electron microscope (SEM)at a magnification of 200 times, and a microstructure picture is takenthereby. Next, in the image thus taken, a line in parallel to the lineat the bottom end of the second member 22 is drawn so as to be incontact with the topmost portion of the porous ceramic. This line thusdrawn is regarded as a reference line (a chain line in FIG. 2), and theintrusion depth at this line is set to 0. Next, the reference line isequally divided into six segments, and five linear lines orthogonal tothe reference line are drawn and are used as measurement lines (lines(1) to (5) in FIG. 2). The intersection between the reference line andeach measurement line is regarded as a starting point, the intersectionbetween the measurement line and the bottom end of the oxide ceramic isregarded as an end point, and the length therebetween is measured foreach of the five measurement lines. The length of each of the five linesin consideration of the magnification used in the picture taking isobtained, and the average value calculated therefrom is regarded as theintrusion depth.

Any dense member having a low porosity may be used as the densematerial, and for example, either a metal member or a dense ceramic maybe used. The dense material may be a material having a porosity of 5percent by volume or less, and the porosity is preferably 1 percent byvolume or less and more preferably 0.5 percent by volume or less.Although the metal member is not particularly limited as long as beingformed of a metal, such as a typical metal or a transition metal, forexample, a metal member having high electrically conductive propertiesis preferable. As the transition metal, a metal, such as Fe, Co, Ni, orCu, and an alloy thereof are preferable. In accordance with theapplication, a noble metal, such as Pt or Au, may also be used. Thismetal member may be used as an electrode, and in this case, for example,stainless steel, such as a Cr—Ni—Fe-based alloy (SUS304) or aCr—Fe-based alloy (SUS430), is preferably used. This metal member ispreferably an alloy containing at least Fe and Cr, and an alloy at leastcontaining 70 to less than 90 percent by mass of Fe and 10 to less than30 percent by mass of Cr is more preferable. The reasons for this arethat the material quality is stable, and the electrically conductiveproperties are excellent. The shape of the metal member may beappropriately selected from a plate or the like in accordance with theapplication. As the dense ceramic, for example, a ceramic obtained bydensely sintering any one of the materials mentioned above as the porousceramic, a member formed by filling a filler or an impregnant in thepores of the porous ceramic, or a composite oxide member containing atleast two types of metals may be mentioned. As the member formed byfilling, in particular, for example, a Si-impregnated SiC sintered bodyin which pores of porous SiC are impregnated with metal Si may bementioned. This material has good thermally conductive properties andalso has good electrically conductive properties due to the presence ofthe metal Si. As the composite oxide member, for example, anelectrically conductive ceramic material, such as a LaCrO₃-basedmaterial, a BaTiO₃-based material, a LaMnO₃-based material, aLaCoO₃-based material, a NaCo₂O₄-based material, a CaCo₄O₉-basedmaterial, a LaNiO₃-based material, or a SrTiO₂-based material, may bementioned. The expression “-based materials” is intended to include amaterial partially replaced with an element, e.g., an alkali metalelement, an alkaline-earth metal element, or an element having adifferent valence number. A specific example of the LaMnO₃-basedmaterials is (La_(0.9)Sr_(0.1))MnO₃.

The first member 21 may be a member formed of an oxide ceramic. That is,as is the joint portion 30 which will be described later, the firstmember may be formed of an oxide ceramic containing a Fe₃O₄ phase inwhich a solute component capable of forming a spinel-type oxide with Feis solid-dissolved. The first member 21 may be an electrode formed on anouter surface of a honeycomb structural body including: a partition wallformed of a porous ceramic which forms and defines a plurality of cellseach functioning as a flow path of a fluid and extending from one endsurface to the other end surface; and an outer circumference wall formedalong the outermost circumference. The first member 21 may be formed ofthe same oxide ceramic as that of the joint portion 30 and may alsofunction as the joint portion 30.

This first member 21 may be formed by thermal spraying. That is, thefirst member 21 may be manufactured by a thermal spraying step in whichafter a raw material powder including a Fe raw material powder whichcontains at least one of a Fe metal powder and a Fe oxide powder and asolute component powder which contains a solute component capable offorming a spinel-type oxide with Fe is melted, the molten raw materialpowder thus obtained is sprayed on a predetermined substrate so as toform a first member 21 formed from an oxide ceramic containing a Fe₃O₄phase in which a solute component is solid-dissolved. As the rawmaterial powder used in the thermal spraying, for example, a powderobtained by mixing a Fe₂O₃ powder and a solute component powder and thengranulating a mixture formed thereby may be used, or a powder formedfrom the powder described above by adding Fe₃O₄ thereto or by replacingFe₂O₃ with Fe₃O₄ may also be used. When the Fe oxide powder is used, thefirst member 21 may be formed from an oxide ceramic containing a Fe₃O₄phase in which a solute component is solid-dissolved. When a Fe₂O₃powder is used, a Fe₃O₄ phase is generated in a thermal sprayingprocess. In this raw material powder, a Fe metal powder may also becontained. As the thermal spraying method, thermal spraying using aflammable gas, such as flame spraying or high-speed flame spraying;thermal spraying using electric energy, such as arc spraying, (DC)plasma spraying, RF plasma spraying, wire explosion spraying, orelectrothermally exploded powder spraying; or thermal spraying usinglaser light, such as laser spraying or laser/plasma spraying, may bementioned, and among those techniques, plasma spraying is preferable. Asthe plasma spraying, for example, air plasma spraying, low pressureplasma spraying, high pressure plasma spraying, under water plasmaspraying, or water stabilized plasma spraying may be mentioned, and theair plasma spraying is simple and preferable.

Alternatively, the first member 21 may be a member formed by firingafter a raw material powder is formed. That is, the first member 21 maybe manufactured by a printing and firing step of forming a first member21 composed of an oxide ceramic containing a Fe₃O₄ phase in which asolute component is solid-dissolved. In the step described above, aftera raw material powder including a Fe raw material powder which containsat least one of a Fe metal powder and a Fe oxide powder and a solutecomponent powder which contains a solute component capable of forming aspinel-type oxide with Fe is formed on a predetermined substrate, firingis performed.

The difference in thermal expansion coefficient between the first member21 and the second member 22 may be set to 4.0 ppm/K or more. Even in ajoined body formed by joining two members having a relatively largedifference in thermal expansion coefficient, by a joint portion formedof an oxide ceramic, the joining strength and the electricallyconductive properties can be maintained. In particular, even in a joinedbody which is to be repeatedly heated while being used, the joiningstrength and the electrically conductive properties can be maintained.The difference in thermal expansion coefficient may be set to 6.0 ppm/Kor more and may also be set to 15 ppm/K or less. For example, as for thethermal expansion coefficient, a Cr—Ni—Fe-based alloy (SUS304) has 18ppm/K, a Cr—Fe-based alloy (SUS430) has 12 ppm/K, a Si-bonded SiCsintered body has 4.6 ppm/K, a Al₂O₃ porous body has 7.0 ppm/K, andLaCrO₃ has 9.4 ppm/K.

The oxide ceramic forming the joint portion 30 may be a Fe oxide inwhich at least one of Mn, Co, Ni, Cu, and Zn is solid-dissolved as asolute component. Those components are each preferable since capable offorming a spinel-type oxide with Fe and likely to be solid-dissolved inFe₃O₄. Among those components, Ni is preferable as the solute component.

In the oxide ceramic, the solute component is preferably solid-dissolvedin a range of 0.5 to 30 percent by mass, more preferably in a range of 1to 25 percent by mass, and further preferably in a range of 1 to 15percent by mass. These ranges are preferable because a high joiningstrength is obtained and the heat resistance is also high.

The oxide ceramic may contain Ni as a solute component, and the peakshift of the (751) plane of Fe₃O₄ measured by x-ray diffraction usingthe CuKα line may be set to 0.02° or more. Accordingly, the oxideceramic can be made more thermally stable. This peak shift is morepreferably 0.05° or more and may also be set to 0.1° or more. Inaddition, this peal shift may be 0.45° or less, and is preferably 0.21°or less. With the peal shift of 0.45° or less, the amount of oxide addedcan be reduced, and decrease of strength can be prevented.

The oxide ceramic may further contain a Fe₂O₃ phase besides a Fe₃O₄phase and may contain Ni as a solute component, and the peak shift ofthe (410) plane of Fe₂O₃ measured by x-ray diffraction using the CuKαline may be set to 0.02° or more. Accordingly, the oxide ceramic can bemade further thermally stable. This peak shift is more preferably 0.04°or more and may also be set to 0.05° or more. In addition, this pealshift may be 0.055° or less. With the peal shift of 0.055° or less, theamount of oxide added can be reduced, and decrease of strength can beprevented.

The oxide ceramic may contain no crystal phase of Fe₂MO₄ (where Mrepresents a solute component). Since this Fe₂MO₄ has low electricallyconductive properties, when a joined body having electrically conductiveproperties is to be formed, the presence of this crystal phase is notpreferable.

In the joint portion 30, a surface layer 31 may be formed of a Fe₂O₃phase, and an inner portion 32 may be formed of a Fe₃O₄ phase.Accordingly, since a chemically and thermally stable Fe₂O₃ phase ispresent at the surface of the joint portion, the thermal stability ofthe Fe₃O₄ phase is likely to be maintained. The surface layer 31 may bea dense layer as compared to the inner portion 32. This surface layer 31may have a porosity of 5 percent by volume or less. This surface layer31 is preferably formed only on a surface to be exposed to the air. Thissurface layer 31 may also be formed of a crystal phase other than theFe₂O₃ phase and may be formed not on the surface to be exposed to theair. In the joint portion 30, the thickness of the surface layer 31 ispreferably 15 μm or less. The thickness of the surface layer 31 may beset to either 10 μm or less or 8 μm or less. In view of thermal andchemical protection of the inner portion 32, the thickness of thesurface layer 31 may be appropriately selected.

The oxide ceramic may contain Fe as a first component which is a primarycomponent of a metal and at least one of Si, Zr, Ti, Sn, Nb, Sb, and Taas a second component. This second component is a component differentfrom the component solid-dissolved in the Fe₃O₄ phase described aboveand may be an auxiliary component to the solute component. When thejoint portion contains the second component, the electrically conductiveproperties are further imparted thereto since the second component isfurther solid-dissolved in Fe₃O₄ of the oxide ceramic; hence, forexample, the degradation in electrically conductive properties caused byuse under heating conditions can be preferably suppressed. It ispreferable that the joint portion contains the second component, becausethe electrical resistance of the joint portion can be further reduced,and heat generation is not likely to occur. The joint portion 30 may beformed, for example, by adding a compound (also called a secondcompound) containing the second component to a raw material containingthe first component. This second compound may also be used as anelectrically conductive auxiliary agent. This second compound may be acarbonate salt, an oxide, a hydroxide, a chloride, and/or a nitratesalt, and among those mentioned above, this second compound may be acarbonate salt or an oxide. In particular, as the second compound, forexample, TiO₂, SnO₂, Nb₂O₅, SiO₂, or ZrO₂ may be mentioned. The contentof the second component is, for example, preferably 5 percent by mass orless on the compounding standard of the joint portion and morepreferably 2 percent by mass or less.

In the oxide ceramic, an oxide of the solute component may co-exist. Forexample, when the primary component of the oxide ceramic is a (Fe,Ni)₃O₄phase, NiO, which is an oxide of the solute component, may also bepresent as a crystal phase, and when the primary component of the oxideceramic is a (Fe,Mn)₃O₄ phase, an oxide, such as MnO, MnO₂, Mn₂O₃,and/or Mn₃O₄, may also co-exist. In the oxide ceramic, a Fe metal mayalso remain.

In the joined body in which the first member 21 and the second member22, each of which has electrically conductive properties, are joined toeach other, the electrical conductivity of the joint portion 30 ispreferably 1×10⁻¹ (S/cm) or more. The electrical conductivity of thejoint portion 30 is more preferably 1 (S/cm) or more and furtherpreferably 10 (S/cm) or more. As the electrical conductivity is higher,the electrically conductive properties are improved, and the electricitycan be efficiently used; however, in consideration of materials to beused in combination, the upper limit may be approximately 10³ (S/cm).The electrical conductivity may be determined by forming holes in partsof the protective layer 14, baking Ag electrodes on exposed portions,bringing probes into contact with the electrodes to measure theelectrical resistance, converting the resulting resistance into volumeresistivity using the area of the electrodes and the interelectrodedistance, and calculating the reciprocal of the volume resistivity.

In the joined body of the present invention, the joining strengthbetween the first member and the second member is preferably 3.5 MPa ormore. The joining strength is measured by a four-point bending test(JIS-R1632). This joining strength is more preferably 5.0 MPa or moreand further preferably 10 MPa or more. As the joining strength isincreased, a stronger joining is obtained, and the reliability ispreferably enhanced; however, in consideration of materials to be usedin combination, the upper limit may be approximately 500 MPa.

The joint portion 30 may be formed by adding a pore forming agent. Thepore forming agent preferably disappears when processed by some type oftreatment, and for example, at least one type selected from the groupconsisting of carbon black, coke, starch, glutinous rice flour, naturalresin, and synthetic resin, which are burnt down by a heat treatment,may be used. For example, the amount of the pore forming agent of thejoint portion is on the volume rate basis, preferably 10 percent byvolume or more and more preferably 20 percent by volume or more. It ispreferable that 10 percent by volume or more of the pore forming agentis used, because the stress relaxation in the joint portion is furtherimproved. The amount of the pore forming agent of the joint portion ison the volume rate basis, preferably 50 percent by volume or less andmore preferably 30 percent by volume of less. It is preferable that 50percent by volume or less of the pore forming agent is used, because thedecrease in mechanical strength of the joint portion can be furthersuppressed. The amount of the pore forming agent of the joint portion ispreferably appropriately selected in accordance with the relationshipbetween the degree of stress relaxation and the mechanical strength ofthe joint portion.

The joint portion 30 may be manufactured by a joining step as describedbelow. After a laminate is formed by forming between the first member 21and the second member 22, a joint layer including a Fe metal powder anda solute component powder which contains a solute component capableforming a spinel-type oxide with Fe, this laminate is fired in a lowtemperature range compared to the melting point of a Fe oxide to form anoxide ceramic, so that the joint portion 30 is formed. In this joiningstep, the joint portion 30 may be formed by firing in the air or byfiring in the air after a heat treatment is performed in a non-oxidizingatmosphere.

Alternatively, the joint portion 30 may be manufactured by a thermalspraying step in which a raw material powder including a Fe raw materialpowder which contains at least one of a Fe metal powder and a Fe oxidepowder and a solute component powder which contains a solute componentcapable of forming a spinel-type oxide with Fe is melted and thensprayed to form the joint portion 30 from a ceramic which joins thefirst member 21 and the second member 22 adjacent thereto. As the rawmaterial powder for thermal spraying, a powder obtained by mixing aFe₂O₃ powder and a solute component powder and then granulating amixture formed thereby may be used, or a powder formed from the powderdescribed above by adding Fe a thereto or by replacing Fe₂O₃ with Fe₃O₄may be used. When a Fe oxide powder is used, the joint portion 30 can beformed from an oxide ceramic containing a Fe₃O₄ phase in which a solutecomponent is solid-dissolved. The details of the thermal spraying aresimilar to those described above, and hence, the description thereofwill be omitted.

The joined body 20 is not particularly limited as long as having thestructure in which the first member 21 and the second member 22 arejoined to each other, and for example, the joined body may be used, forexample, for a honeycomb structural body, a thermoelectric element, aceramic heater, or a gas sensor for oxygen, NO_(x), or the like. Forexample, in the case of the honeycomb structural body, the joined bodymay be preferably used as a device or the like which heats the honeycombstructural body by applying the voltage to metal members. The firstmember may be a part of a honeycomb structural body including: apartition wall formed of a porous ceramic which forms and defines aplurality of cells each functioning as a flow path of a fluid andextending from one end surface to the other end surface; and an outercircumference wall formed along the outermost circumference. The secondmember 22 may be a metal member. As shown in FIG. 3, a honeycombstructural body 40 is configured to heat a honeycomb substrate 41 byapplying the voltage between electrode portions 45. This honeycombstructural body 40 includes the honeycomb substrate 41, a highelectrically conductive portion 42 having high electrically conductiveproperties as compared to those of the honeycomb substrate 41, and theelectrode portions 45 connected to the high electrically conductiveportion 42. The electrode portion 45 includes an electrode terminalprotrusion portion 51 connected to the high electrically conductiveportion 42, a metal terminal portion 52 which is a metal member, and ajoint portion 50 electrically and mechanically connecting the electrodeterminal protrusion portion 51 and the metal terminal portion 52. Thisjoint portion 50 is formed of an oxide ceramic as is the joint portion30. That is, the first member 21 is the electrode terminal protrusionportion 51 which is formed to have a convex shape or a concave shape,the second member 22 is the metal terminal portion 52 which is formed sothat a portion to be joined to the electrode terminal protrusion portion51 has a concave shape or a convex shape complementary to the shape ofthe electrode terminal portion, and the joint portion 50 electricallyconnects the electrode terminal protrusion portion 51 and the metalterminal portion 52 at a portion between the concave shape and theconvex shape at which the electrode terminal protrusion portion 51 andthe metal terminal portion 52 are engaged with each other. In this case,as shown by an electrode portion 455 of FIG. 4, the electrode terminalprotrusion portion 51 and the metal terminal portion 52 may form nospace between a protruding front end of the convex shape and a bottompart of the concave shape, those shapes being complementary to eachother, and the joint portion 50 may electrically connect the electrodeterminal protrusion portion 51 and the metal terminal portion 52 at sidesurface portions of the concave shape and the convex shape at which theelectrode terminal protrusion portion 51 and the metal terminal portion52 are engaged with each other. For example, when the honeycombstructural body is formed of a Si-bonded SiC ceramic, the highelectrically conductive portion 42 may have a higher metal Si content.

Next, a honeycomb structural body of the present invention will bedescribed in detail. FIG. 5 is an explanatory view of a honeycombstructural body 40B. This honeycomb structural body 40B includes: apartition wall 48 formed of a porous ceramic which forms and defines aplurality of cells 47 each functioning as a flow path of a fluid andextending from one end surface to the other end surface; and an outercircumference wall 49 formed along the outermost circumference. For thishoneycomb structural body 40B, an oxide ceramic containing a Fe₃O₄ phasein which a solute component capable of forming a spinel-type oxide withFe is solid-dissolved is formed. This oxide ceramic may be used aselectrodes 44 each formed on an outer surface of the honeycombstructural body 40B. When the electrode 44 is formed of this oxideceramic, the heat resistance and the oxidation resistance can be furtherimproved, and the decrease in electrically conductive properties can befurther suppressed. The honeycomb structural body 40B is provided withthe electrodes 44, each of which functions as the first member, formedon the outer surface (surface of the outer circumference wall 49) of thehoneycomb structural body 40B and terminals 46, each of which functionsas the second member, and the oxide ceramic may be used as the jointportion 30 which joins the first member and the second member. When thisoxide ceramic is used as the joint portion 30, the heat resistance andthe oxidation resistance can be further improved, more reliable joiningcan be obtained, and the decrease in electrically conductive propertiescan be further suppressed. Furthermore, the electrode 44 and the jointportion 30 each may be formed from this oxide ceramic. This oxideceramic may be formed for the honeycomb structural body 40B by thermalspraying. Accordingly, the oxide ceramic containing a Fe₃O₄ phase inwhich a solute component is solid-dissolved can be more easily formed.Alternatively, the oxide ceramic may be obtained by firing after the rawmaterial powder is formed on the honeycomb structural body (or theelectrode 44). In this honeycomb structural body 40B, the difference inthermal expansion coefficient between the first member and the secondmember may be set to 4.0 ppm/K or more. When the joint portion 30 isformed from this oxide ceramic, even if the difference in thermalexpansion coefficient is large as described above, more reliable joiningcan be obtained.

In the honeycomb structural body of the present invention, the oxideceramic may be the electrode 44 formed on the outer surface of thehoneycomb structural body so that a ratio (L1/L) of a length L1 of theoxide ceramic to a total length L of the honeycomb structural body in aflow path direction is in a range of 0.1 to 1, and a ratio (X1/X) of alength X1 of the oxide ceramic to an outer circumference length X of thesurface of the honeycomb structural body perpendicular to the flow pathis in a range of 0.02 to 0.3. FIG. 6 includes explanatory views of thetotal length L of the honeycomb structural body, the length L1, theouter circumference length X, and the length X1; FIG. 6A is a top planview; and FIG. 65 is a side view. When L1/L is 0.1 or more, the heatgeneration distribution can be made more uniform. When X1/X is 0.02 ormore, the heat generation distribution can be made more uniform. WhenX1/X is 0.3 or less, the decrease in heat shock resistance can befurther suppressed. When the electrode 44 formed from this oxide ceramicis in the range described above, by voltage application, electricity canbe more uniformly supplied to the honeycomb substrate 41. The length L1in the flow path direction may be set in a range of 10 to 90 mm. Theouter circumference length X1 of the surface of the electrode 44perpendicular to the flow path is preferably set to ¼ or less of thehoneycomb outer circumference length X and is preferably set in a rangeof 5 to 70 mm. A thickness t of the electrode 44 is preferably in arange of 10 to 500 μm. When the thickness t is 10 μm or more, since theapparent resistance is decreased, the heat generation distribution canbe made more uniform. When the thickness t is 500 μm or less, thedifference in thermal expansion coefficient between the substrate andthe electrode can be further reduced, and the decrease in heat shockresistance can be further suppressed. This electrode 44 may be formed sothat a ratio (S1/S) of an area S1 of the electrode to a total area S ofthe outer side surface of the honeycomb structural body is 0.002 to 0.3.When the electrode 44 is formed in the range described above, by voltageapplication, electricity can be more uniformly supplied to the honeycombsubstrate 41. Since the solute component, the peak shift, and the likeare similar to those of the joined body described above, the descriptionthereof will be omitted.

According to the honeycomb structural body of the present invention, asshown in FIG. 7, there may be provided the electrode 44, which is thefirst member 21, formed on an outer surface of a honeycomb structuralbody 40C, the terminal 46, which is the second member 22, adjacent tothe electrode 44, and a joint portion 30C which is formed of an oxideceramic and which joins the electrode 44 and the terminal 46 by coveringthereof. That is, a joined body 20C of the present invention may includethe first member 21, the second member 22 adjacent thereto, and thejoint portion 30C joining the first member 21 and the second member 22by covering thereof. According to the structure described above, the twomembers can also be joined to each other with high reliability. Thedecrease in electrically conductive properties can be furthersuppressed. In this joined body 20C, the joint portion 30C may be formedin such a way that a raw material powder of the joint portion 30C ismelted and then sprayed to the electrode 44, which is the first member21, formed on the outer surface of the honeycomb structural body 40C andthe terminal 46, which is the second member 22, adjacent to theelectrode 44 so as to join the electrode 44 and the terminal 46 bycovering thereof.

The honeycomb structural body of the present invention may be ahoneycomb filter in which the cells are formed so that the end portionsthereof are not sealed or so that the end portions thereof arealternately sealed. The honeycomb structural body may be integrallyformed or may be formed in such a way that after rectangularparallelepiped honeycomb segments are joined to each other, the outerdiameter thereof is machined to have a cylindrical shape.

Next, a method for manufacturing a joined body of the present inventionwill be described. The method for manufacturing a joined body of thepresent invention may include, for example, a joining step of forming alaminate in which a joint layer including a Fe metal powder and a solutecomponent powder which contains a solute component capable of forming aspinel-type oxide with Fe is formed between a first member and a secondmember, and a firing this laminate in a temperature range lower than themelting point of a Fe oxide to form an oxide ceramic functioning as ajoint portion which joins the first member and the second member.

(Joining Step)

As a material used for the joint portion, a Fe metal powder and a solutecomponent powder containing a solute component capable of forming aspinel-type oxide with Fe may be mentioned. As the solute component, atleast one of Mn, Co, Ni, Cu, and Zn may be mentioned. The solutecomponent may be, for example, a metal powder or an oxide powdercontaining a solute component. Ss for Fe, since a Fe oxide is not ableto form a sufficient joint between the first member and the secondmember even by a heat treatment, the Fe oxide is not suitable for theraw material of the joint portion. As this raw material powder, a powderhaving an average particle diameter of 1 to 40 μm is preferably used. Inthe range described above, an appropriate joining strength is likely tobe obtained. The average particle diameter of the raw material of thisjoint portion is preferably 30 μm or less, more preferably 10 μm orless, and further preferably 5 μm or less. This average particlediameter is more preferably 3 μm or more. The average particle diameterof this raw material powder indicates the median diameter (D50) measuredby a laser diffraction/scattering particle size distribution measurementapparatus using water as a dispersion medium.

In this step, at least two raw material powders having differentparticle sizes are preferably mixed together to form a raw materialpowder of the joint portion. Accordingly, the joining strength at thejoint portion can be further increased. The Fe metal powder may beprepared by mixing a first powder having a predetermined averageparticle diameter (μm) and a second powder having an average particlediameter (μm) larger than the predetermined average particle diameter.The second powder is preferably used in order to improve the strength ofthe joint portion itself. The average particle diameter of the firstpowder may be set in a range of 0.1 to 10 (μm), and the average particlediameter of the second powder may be set in a range of 10 to 100 (μm).The addition amount of the solute component is, for example, as thecomposition rate to the total of the joint portion, preferably 0.5percent by mass or more, more preferably 1 percent by mass or more, andfurther preferably 2 percent by mass or more. This addition amount ofthe solute component as the composition rate to the total of the jointportion is preferably 30 percent by mass or less, more preferably 25percent by mass or less, and further preferably 15 percent by mass orless.

In the joining step, the laminate may be fired in the air or may befired in the air after a heat treatment is performed in a non-oxidizingatmosphere. As the non-oxidizing atmosphere, for example, a nitrogenatmosphere or a rare gas atmosphere (Ar or He) may be mentioned. Anyjoining temperature (firing temperature) may be selected as long asbeing in a lower temperature range than the melting point of a Fe oxide,and a temperature of 400° C. to 900° C. is preferable. In thistemperature range, the joint layer can be oxidized into an oxideceramic. Although this joining temperature is set in an appropriaterange in accordance with the material of the joint portion, the joiningtemperature is more preferably 500° C. or more and further preferably600° C. or more. The joining temperature is more preferably 850° C. orless and further preferably 800° C. or less. This joining temperature ispreferably higher in view of sufficient oxidation and is preferablylower in view of energy consumption. As described above, a joiningtreatment can be performed in a simple atmosphere, such as in the air,and at a low temperature, such as 900° C. or less. In this step, thefiring is preferably performed so that the porosity of the oxide ceramicis 60 percent by volume or less, and the porosity is more preferably 50percent by volume or less and further preferably 30 percent by volume orless. The oxide ceramic is more preferably a dense body in view of thejoining strength. In this step, the firing is preferably performed sothat the porosity of the oxide ceramic is 5 percent by volume or more,more preferably performed so that the porosity is 10 percent by volumeor more, and further preferably performed so that the porosity is 20percent by volume or more. The oxide ceramic more preferably has poresin view of stress relaxation.

In the joining step, a surface layer containing a Fe₂O₃ phase may beformed in the joint portion. This surface layer may be formed, forexample, by the following method. After the raw material powder of thejoint portion is formed into a paste, this joining material paste isformed on the first member and/or the second member and is then held inthe air at 750° C. for 1 hour for firing, so that a double layerstructure including the surface layer and the inner portion can beformed. The thickness of the surface layer can be controlled by a firingtemperature and a holding time. When the temperature is increased, thethickness of the surface layer is increased, and when the holding timeis increased, the thickness of the surface layer is increased. Inparticular, when the thickness of the joining material paste is 300 μm,the firing temperature is preferably 1,000° C. or less. When thetemperature is 1,000° C. or less, excessive oxidation so as to form nodouble layer structure can be more suppressed. This firing temperatureis preferably 300° C. or more. The reason for this is that when thetemperature is 300° C. or more, oxidation is sufficiently performed. Inthe case in which firing is performed using a common atmosphere furnace,the holding time of the firing is preferably 24 hours or less. When thetime is more than 24 hours, since the growth of the surface layer isalmost stopped, a shorter holding time than that mentioned above ispreferable in consideration of production cost and material amounts. Theholding time is preferably 10 minutes or more. The reason for this isthat when the time is 10 minutes or more, a sufficient surface layer canbe formed. Alternatively, as a method for forming the surface layer, forexample, the joining material paste is formed on the first member and/orthe second member and is then held in Ar at 750° C. for 1 hour forfiring, so that a Fe₃O₄ single phase is obtained. Subsequently, theFe₃O₄ single phase thus obtained may be held in the air at 750° C. for0.5 hours so as to form the surface layer. The thickness of the surfacelayer can be controlled by a firing temperature and a holding time inthe air. The firing temperature in the air is preferably in a range of300° C. to 1,000° C. as in the case described above.

In this step, besides the first component, which is a metal as a primarycomponent, and the solute component, a compound (second compound)containing a second component which is a metal element is preferablyadded to the raw material powder of the joint portion. This secondcompound may be used as an electrically conductive auxiliary agent. Asthe second compound, for example, TiO₂, SnO₂, Nb₂O₅, SiO₂, or ZrO₂ maybe mentioned.

In this step, a pore forming agent may be added to the raw materialpowder of the joint portion. For example, the amount of the pore formingagent of the joint portion is on the volume rate basis, preferably 10percent by volume or more and more preferably 20 percent by volume ormore. When 10 percent by volume or more of the pore forming agent isused, it is preferable since the stress relaxation in the joint portionis further improved. The amount of the pore forming agent of the jointportion is on the volume rate basis, preferably 50 percent by volume orless and more preferably 30 percent by volume of less. When 50 percentby volume or less of the pore forming agent is used, it is preferablesince the decrease in mechanical strength of the joint portion can befurther suppressed. The amount of the pore forming agent of the jointportion may be appropriately selected in accordance with therelationship between the degree of stress relaxation and the mechanicalstrength of the joint portion.

In the step described above, firing is preferably performed while themovement of the first member 21 and the second member 22 is restricted.Accordingly, the displacement of the members can be prevented. Inaddition, it is believed that the first member 21 and the second member22 can be more reliably joined to each other. Incidentally, the term“restriction of movement” may include, for example, the case in which ametal member is fixed by applying a load thereto which may be given by aholding jig or the like. Although it is possible to fix the first member21 and the second member 22 by positively applying a pressure, thetreatment as described above is preferably omitted in view ofsimplification of the manufacturing step.

Next, a method for manufacturing a honeycomb structural body will bedescribed. This manufacturing method is a method for manufacturing ahoneycomb structural body including a partition wall formed of a porousceramic which forms and defines a plurality of cells each functioning asa flow path of a fluid and extending from one end surface to the otherend surface and an outer circumference wall formed along the outermostcircumference. This manufacturing method includes a forming step of, byusing a raw material powder including a Fe raw material powder whichcontains at least one of a Fe metal powder and a Fe oxide powder and asolute component powder which contains a solute component capable offorming a spinel-type oxide with Fe is melted, forming an oxide ceramiccontaining a Fe₃O₄ phase in which a solute component is solid-dissolvedis formed for the honeycomb structural body. In this forming step, theoxide ceramic layer may be formed on an outer surface of the honeycombstructural body. The forming step may be a thermal spraying step of,after the raw material powder is melted, thermal spraying the rawmaterial powder. Otherwise, the forming step may be a firing step of,after the raw material powder is formed on the honeycomb structuralbody, firing the ram material powder. The thermal spraying step may be astep of, after the raw material powder is melted, forming a jointportion of an oxide ceramic which joins an electrode, which is the firstmember, formed on the outer surface of the honeycomb structural body anda terminal, which is the second member, adjacent to the electrodedescribed above.

As the raw material powder used in the forming step, a powder obtainedby mixing a Fe₂O₃ powder and a solute component powder and thengranulating a mixture formed thereby may be used, or a powder formed byadding Fe₃O₄ to the powder described above or by replacing Fe₂O₃ withFe₃O₄ may be used. When the Fe oxide powder is used, the electrode andthe joint portion may be formed from an oxide ceramic containing a Fe₃O₄phase in which a solute component is solid-dissolved. The raw materialpowder may further contain a Fe metal powder. When the Fe₂O₃ powder isused in the thermal spraying step, a Fe₃O₄ phase is generated in thethermal spraying process. As the thermal spraying method, for example,thermal spraying using a flammable gas, such as flame spraying orhigh-speed flame spraying; thermal spraying using electric energy, suchas arc spraying, (DC) plasma spraying, RF plasma spraying, wireexplosion spraying, or electrothermally exploded powder spraying; orthermal spraying using laser light, such as laser spraying orlaser/plasma spraying, may be mentioned, and among those techniques,plasma spraying is preferable. As the plasma spraying, for example, airplasma spraying, low pressure plasma spraying, high pressure plasmaspraying, under water plasma spraying, or water stabilized plasmaspraying may be mentioned, and the air plasma spraying is simple andpreferable. In addition, a raw material powder having a particle sizeD90 of 150 to 1,000 μm, a particle size D50 of 20 to 150 and a particlesize D10 of 10 μm or less is preferably used. When plasma spraying isperformed, as the thermal spraying conditions, an Ar gas may be used, orH₂ may be added thereto. Plasma spraying may be performed at a currentof 600 to 1,000 A and a voltage of 30 to 100 V.

Alternatively, the oxide ceramic layer may be obtained by firing afterthe raw material powder is formed on a honeycomb substrate. That is, theoxide ceramic layer may be formed by a printing and firing step in whichafter a raw material powder including a Fe raw material powder whichcontains at least one of a Fe metal powder and a Fe oxide powder and asolute component powder which contains a solute component capable offorming a spinel-type oxide with Fe is formed on a honeycomb substrate,firing is performed so as to form an oxide ceramic layer containing aFe₃O₄ phase in which a solute component is solid-dissolved. In theprinting and firing step, after the raw material powder is formed on thehoneycomb substrate, a heat treatment may be performed. Accordingly, theheat resistance can be further improved. This heat treatment may beperformed in the air at 700° C. to 950° C. and more preferably at 800°C. to 850° C. In this heat treatment, the temperature described abovemay be held for 30 minutes to 2 hours and more preferably for 1 hour.

In the forming step (the thermal spraying step and the printing andfiring step), when the oxide ceramic layer serves as an electrode, asdescribed above, the electrode may be formed on the outer surface of thehoneycomb structural body so that the ratio (L1/L) of the length L1 ofthe electrode to the total length L of the honeycomb structural body ina flow path direction is in a range of 0.1 to 1 and the ratio (X1/X) ofthe length X1 of the electrode to the outer circumference length X ofthe surface of the honeycomb structural body perpendicular to the flowpath is in a range of 0.02 to 0.3. In this step, the electrode may beformed so that the ratio (S1/S) of the area S1 of the electrode to thetotal side surface area S of the outer surface of the honeycombsstructural body is in a range of 0.002 to 0.3.

According to the joined body of the embodiment and the method formanufacturing the same described above, the first member and the secondmember are joined to each other with an oxide ceramic containing a Fe₃O₄phase in which a solute component capable of forming a spinel-type oxidewith Fe is solid-dissolved. In this oxide ceramic, Fe₃O₄ is thermallystabilized by the solute component. Hence, the two members can be morereliably joined to each other. In the manufacturing method of the joinedbody, a joint layer including a Fe metal powder and a solute componentpowder containing a solute component capable of forming a spinel-typeoxide with Fe is formed and then fired, so that the two members can bejoined to each other by a simple step.

According to the honeycomb structural body of the embodiment and themethod for manufacturing the same described above, an oxide ceramiccontaining a Fe₃O₄ phase in which a solute component capable of forminga spinel-type oxide with Fe is solid-dissolved is formed. In this oxideceramic, Fe₃O₄ is thermally stabilized by the solute component. Hence,the decrease in electrically conductive properties can be furthersuppressed. In this manufacturing method, the raw material powder can besprayed, and in this case, a Fe₃O₄ phase, which is a high-temperaturestable phase, is likely to be generated, and an oxide ceramic containinga Fe₃O₄ phase can be more easily formed.

The present invention is not limited at all to the embodiments describedabove and may be performed in various modes without departing from thetechnical scope of the present invention.

EXAMPLES

Hereinafter, examples in each of which the joined body of the presentinvention was actually manufactured will be described as experimentalexamples. Experimental Examples 26 to 36, 39 to 45 correspond toexamples of the present invention, Experimental Examples 24, 25, 37, and38 correspond to comparative examples, and Experimental Examples 1 to 23correspond to reference examples.

Formation Method

A first member and a second member were prepared. A metal powder of Fe,a metal powder of Ni, Mn, Co, Cu, or Zn or an oxide powder thereof, apoly(vinyl butyral) resin (PVB) as a binder, and terpineol as a solventwere mixed together to form a joining material paste. To the joiningmaterial paste, a second compound (TiO₂) and/or a pore forming agent(starch) was added in accordance with each sample. The Fe metal powderused as a raw material was prepared by mixing a powder (fine powder)having an average particle diameter 3 μm and a powder (coarse powder)having an average particle diameter of 35 μm at an appropriatecomposition ratio. This joining material paste was applied to the firstand the second members, each of which was an object to be joined, andthose members were adhered to each other with the paste providedtherebetween. A sample obtained by adhesion as described above was leftin the air at 80° C. over one night, so that terpineol was sufficientlydried. A holding jig was placed on this sample so as to prevent thedisplacement of the two members and was fired (joined) in the air at200° C. to 800° C. As a firing atmosphere, an air atmosphere or anon-oxidizing atmosphere was used. When the heat treatment was performedin a non-oxidizing atmosphere (Ar), firing was then performed in the airat 200° C. to 800° C.

Formation of First Member

As a porous ceramic, a Si-bonded SiC sintered body was formed. As a rawmaterial of the porous ceramic of the Si-bonded SiC sintered body, a“mixed powder” was formed by mixing a SiC powder and a metal Si powderat a volume ratio of 38:22. To the “mixed powder” described above, ahydroxypropyl methylcellulose as a binder, a starch as a pore formingagent, and a water absorptive resin were added together with water, sothat a raw material (molding raw material) for forming a porous materialwas obtained. The molding raw material was kneaded, so that acylindrical molding precursor was formed. The cylindrical moldingprecursor thus obtained was molded by extrusion using an extruder, sothat a honeycomb molded body was formed. This molded body was dried inan air atmosphere at 120° C. to form a dried body. This dried body wasdegreased in an air atmosphere at 450° C. and was then fired in an Aratmosphere at 1,450° C. at a normal pressure for 2 hours. From ahoneycomb porous ceramic obtained as described above, a rectangularparallelepiped sample having a size of 10×20×35 mm was obtained bycutting, so that a substrate (porous ceramic) was obtained. Thissubstrate had a porosity of 40 percent by volume measured by a mercuryintrusion method using a mercury porosimeter (Autopore 1V9520,manufactured by Micromeritics Corp.) and an average pore diameter of 10measured by a method similar to that described above.

As a dense ceramic, a Si-impregnated SiC sintered body in which metal Siwas impregnated in a SiC sintered boy and a ceramic material of LaCrO₃,which was a composite oxide, were formed. For the Si-impregnated SiCsintered body, a hydroxypropyl methylcellulose as a binder, a starch asa pore forming agent, and a water absorptive resin were added togetherwith water to a SiC powder as a raw material, so that a raw material(molding raw material) for forming a porous material was obtained. Themolding raw material was kneaded to obtain a cylindrical moldingprecursor and was then molded by extrusion using an extruder, so that abar-shaped molded boy (10×20×35 mm) was formed. After this molded bodywas dried in an air atmosphere at 120° C. and was then degreased in anair atmosphere at 450° C., firing was performed in an Ar atmosphere at1,450° C. at a normal pressure for 2 hours. A porous ceramic obtained asdescribed above was impregnated with metal Si, so that a substrate(dense ceramic) was obtained. The impregnation treatment was performedas described below. First, metal Si pellets were placed on a porousceramic in a reduced-pressure atmosphere at 1,500° C., so that the metalSi was impregnated into the porous ceramic by a capillary phenomenon.Subsequently, after the atmospheric pressure was obtained byintroduction of Ag, cooling was performed, so that a Si-impregnated SiCsintered body was obtained. This substrate had a porosity of 0.1 percentby volume or less measured by a mercury intrusion method using a mercuryporosimeter. For TaCrO₃, lanthanum oxide and chromium oxide were mixedat an equivalent molar ratio, and this mixture was formed into abar-shaped molded body (10×20×35 mm) by press molding. This molded bodywas fired in an air atmosphere at 1,600° C. for 2 hours, so that asintered body was obtained. The porosity of the Si-impregnated SiCsintered body and that of the composite oxide member measured by amercury intrusion method using a mercury porosimeter were each 0.1percent by volume or less.

Second Member

As the second member, a stainless steel material (SUS) was prepared. Asthe stainless steel material, a Cr—Fe-based alloy (SUS430) was used.This metal member was cut into a bar having a size of 3×4×20 mm, andthis cut sample was used for experiments. The metal member had aporosity of 0.1 percent by volume or less measured by a mercuryintrusion method using a mercury porosimeter.

Experimental Examples 1 to 23

In Experimental Examples 1 to 23, the formation was performed under theconditions shown in Table 1. In Experimental Examples 1 to 10, thecomposition ratio of Ni, which was the solute component, was changed. InExperimental Examples 11 to 13, a Fe₂O₃ phase used as the surface layerwas not formed. In Experimental Example 14, the pore forming agent wasadded, and in Experimental Example 15, a Ni metal powder was used as aNi source. In Experimental Examples 16 to 19, an element other than Niwas uses as the solute component. In Experimental Example 20, a Fe oxidewas used as the joining material raw material. In Experimental Examples21 to 23, the first member was changed.

(Identification of Crystal Phase and Calculation of Peak Shift)

By the use of a rotating anticathode-type x-ray diffraction apparatus(RINT, manufactured by Rigaku Corp.), an x-ray diffraction pattern ofthe joint portion was obtained. The x-ray diffraction measurement wasperformed using a CuKα line source at 50 kV, 300 mA, and 2θ=40° to 120°.The measurement was performed using a powder mixed with Si as theinternal reference, a peak shift amount of the measurement sample wascalculated using the peak of the (220) plane of Si as the reference peakand was used as an index indicating the degree of solid solution of aforeign element. The peak shift amount was obtained using the peak ofthe (410) plane of Fe₂O₃ and the (751) plane of Fe₃O₄. FIG. 8 shows themeasurement results of the x-ray diffraction of Experimental Examples 2and 3.

(Electrical Conductivity of Joining Material)

After a hole having a diameter of 5 mm was formed in a part of the jointportion of the joined body so as to expose a joining material. An Agelectrode having a diameter of 3 mm was baked on the exposed joiningmaterial portion, and the electrical resistance was measured by bringinga measurement needle into contact therewith. The resistance thusmeasured was converted into the volume resistivity using the electrodearea and the distance between terminals, and the reciprocal thereof wasobtained as the electrical conductivity. An electrical conductivity of10 S/cm or more obtained as described above was ranked as “A”, anelectrical conductivity of 0.1 to less than 10 S/cm was ranked as “B”,an electrical conductivity of 0.01 to less than 0.1 S/cm was ranked as“C”, and an electrical conductivity of less than 0.01 S/cm or anelectrical conductivity which could not be measured was ranked as “D”.

(Bending Strength of Joining Material)

The joining strength of the joined body was evaluated by a four-pointbending test in accordance with JIS-R1632. In Experimental Examples 1 to20, after two Si-bonded SiC-made honeycomb bodies each obtained bycutting to have a size of 10×20×40 mm and a SUS430 plate having athickness of 0.05 mm were joined together using the joining materialdescribed above to form the joined body, evaluation was performed byapplying a load thereto. FIG. 9 is an explanatory view of a joined body60 for mechanical strength measurement. The second member 22 is a SUS430plate. In Experimental Example 21, after two Si-impregnated SiC-madehoneycomb bodies each obtained by cutting to have a size of 10×20×40 mmand a SUS430 plate having a thickness of 0.05 mm were joined togetherusing the joining material described above to form the joined body,evaluation was performed by applying a load thereto.

In Experimental Example 22, after two Al₂O₃-made porous material bodieseach obtained by cutting to have a size of 10×20×40 mm and a SUS430plate having a thickness of 0.05 mm were joined together using thejoining material described above to form the joined body, evaluation wasperformed by applying a load thereto. In Experimental Example 23, aftertwo LaCrO₃-made dense material bodies each obtained by cutting to have asize of 10×20×40 mm and a SUS430 plate having a thickness of 0.05 mmwere joined together using the joining material described above to formthe joined body, evaluation was performed by applying a load thereto. Asfor the evaluation of the joining strength, a joining strength of 3.5MPa or more was ranked as “A”, a joining strength of 2.0 to less than3.5 MPa was ranked as “B”, and a joining strength of less than 2.0 MPaor a joining strength which could not be measured was ranked as “D”.Incidentally, a joining strength of 3.5 MPa is a mechanical strength ofa Si-bonded SiC sintered body, and hence, the joining strength of thesample ranked as “A” was higher than the mechanical strength describedabove.

(Heat Resistance Test)

In a heat resistance test, after the sample was held in the air at 850°C. for 24 hours, evaluation was performed by measuring the electricalconductivity and the bending strength of the joining material. As forthe heat resistance evaluation, before and after the heat resistancetest, when the joining strength or the electrical conductivity wasranked as “B” or more, and the evaluation thereof was not changed, thissample was ranked as “A”. In the case in which the joining strength orthe electrical conductivity was changed, although the joining strengthand the electrical conductivity were changed, when the evaluationsthereof were ranked as “B” or more, this sample was ranked as “B”.Although the electrical conductivity was changed, when the evaluationthereof was ranked as “C” or more, this sample was ranked as “C”. Inaddition, although the joining strength was changed, when the evaluationthereof was ranked as “D”, and although the electrical conductivity waschanged, when the evaluation thereof was ranked as “D”, this sample wasranked as “D”.

(Comprehensive Evaluation)

In accordance with the measurement results described above, thecomprehensive evaluation of each sample was performed. The evaluationresult of each joined body before the heat resistance test was regardedas the initial propertie evaluation. In this initial propertieevaluation, when the electrical conductivity was ranked as “A”, and thejoining strength was also ranked as “A”, this sample was ranked as “A(excellent)”. When the joining strength was ranked as “A”, and theelectrical conductivity was ranked as “B”, or when the joining strengthwas ranked as “B”, and the electrical conductivity was ranked as “A” or“B”, this sample was ranked as “B (good)”. When the joining strength orthe electrical conductivity was ranked as “C”, this sample was ranked as“C (fair)”. In addition, when the joining strength or the electricalconductivity was ranked as “D”, this sample was ranked as “D (no good)”.The evaluation after the heat resistance test was performed in the samemanner as described above. For the comprehensive evaluation, when theinitial propertie evaluation and the heat resistance evaluation wereranked as “A”, this sample was ranked as “A”. In addition, when at leastone of the initial propertie evaluation and the heat resistanceevaluation was ranked as “B” or more, that is, when the two evaluationswere ranked as “A” and “B”, “B” and “A”, or “B” and “B”, this sample wasranked as “B”. In addition, when at least one of the initial propertieevaluation and the heat resistance evaluation was ranked as “C”, thatis, when the two evaluations were ranked as “C” and “A”, or “C” and “C”,this sample was ranked as “C”. Furthermore, when at least one of theinitial propertie evaluation and the heat resistance evaluation wasranked as “D” or could not be measured, this sample was ranked as “D”.

TABLE 1 Raw Material for Joining Material (Mixed)/mass % Experi- FeFiring mental First Second Fine Coarse Pore Firing Temper- Exam- Mem-Mem- Pow- Pow- Forming Atmo- ature ples ber ber der der Fe₃O₄ TiO₂ NiONi CuO ZnO Mn₃O₄ CoO Total Agent sphere ° C. 1 Si- SUS 59.3 39.6 1.1100.0 Air 750 2 bonded 60.0 40.0 100.0 Ar 750 3 SiC 39.8 59.7 0.5 100.0Air 750 4 38.8 58.2 1.1 1.9 100.0 Air 750 5 39.2 58.8 2.0 100.0 Air 7506 37.4 56.1 6.6 100.0 Air 750 7 34.8 52.2 12.9 100.0 Air 750 8 30.0 45.025.1 100.0 Air 750 9 26.4 39.7 0.7 33.2 100.0 Air 750 10 19.9 29.8 0.549.8 100.0 Air 750 11 39.2 58.8 2.0 100.0 Ar 750 12 37.4 56.1 6.6 100.0Ar 750 13 34.8 52.2 12.9 100.0 Ar 750 14 39.2 58.8 2.0 100.0 14.0 Air750 15 39.3 58.9 1.8 100.0 Air 750 16 58.2 38.8 1.1 2.0 100.0 Air 750 1758.2 38.8 1.1 2.0 100.0 Air 750 18 58.2 38.8 1.1 2.0 100.0 Air 750 1958.2 38.8 1.1 2.0 100.0 Air 750 20 97 3 100.0 Ar 750 21 Si- 39.2 58.82.0 100.0 Air 750 impreg- nated SiC 22 Al₂O₃ 39.2 58.8 2.0 100.0 Air 75023 LaCrO₃ 39.2 58.8 2.0 100.0 Air 750

(Results and Discussion)

The measurement results of Experimental Examples 1 to 23 arecollectively shown in Table 2. In Table 2, the crystal phases of thesurface layer and the inner portion of the joint portion (oxideceramic), the peak shift amount, the thickness and the porosity of thesurface layer, the initial properties and the evaluation thereof, thecharacteristics after the heat resistance test and the evaluationthereof, and the comprehensive evaluation are collectively shown. Asshown in Table 2, it was found that in Experimental Examples 3 to 8, 11to 19, and 21 to 23, in each of which the peak shift of the Fe₃O₄ phaseoccurred (solute component was solid-dissolved), and no Fe₂MO₄ wascontained, the electrical conductivity and the heat resistance wereexcellent. In this case, it was also found that, the second compound(TiO₂) and the pore forming agent may be contained, the surface layermay contain no Fe₂O₃ phase, and the member to be joined may be either aporous ceramic or a dense body. In addition, it was also found that whenCu, Zn, Mn, Co, and/or the like was used as a solute component insteadof Ni, good results could be obtained.

TABLE 2 Initial Properties Crystal Phase Electrical Experi- of JoiningAmount of Thickness Porosity Conductivity of mental Material¹⁾ PeakShift of Surface of Surface Inside of Joining Joining Exam- SurfaceInternal Fe₃O₄ Fe₂O₃ Layer Layer Material Strength Initial ples LayerPortion ° ° μm % S/cm Evaluation Evaluation Evaluation 1 A B None None3.8  0.5 B A B 2 B None None 1.6 B A B 3 C D 0.028 0.000 14.3  2.50 3.3B A B 4 C D 0.051 0.021 5.6 0.38 25.0 A A A 5 C D 0.060 0.022 5.9 0.4114.7 A A A 6 C D 0.101 0.040 7.7 0.51 55.6 A A A 7 C D 0.203 0.050 8.00.48 33.3 A A A 8 C D 0.225 0.052 8.2 0.52 5.0 B B B 9 A, D, E 0.2180.048 None 0.0 D   D²⁾ D 10 A, D, E 0.221 0.046 0.0 D   D²⁾ D 11 None D0.102 None 26.6 A A A 12 None D 0.202 66.1 A A A 13 None D 0.4064 37.0 AA A 14 C D 0.1 None None 3.6 B B B 15 C D 0.054 0.023 4.8 0.51 26.3 A AA 16 F G 0.061 0.031 5.0 0.62 26.3 A A A 17 F G 0.058 0.028 5.1 0.5827.8 A A A 18 F G 0.050 0.021 4.8 0.60 22.2 A A A 19 F G 0.051 0.022 5.30.61 23.8 A A A 20 Not Joined 21 C D 0.058 0.021 6.1 0.39 18.1 A A A 22C D 0.061 0.025 5.8 0.41 14.2 A A A 23 C D 0.056 0.023 5.9 0.40 17.1 A AA Properties After Heat Resistance Test Electrical Evaluation Experi-Thickness Conductivity After Heat mental Crystal Phase of Surface ofJoining Joining Resistance Overall Exam- Surface Inner Layer MaterialStrength Test Evaluation ples Layer Portion μm S/cm EvaluationEvaluation Evaluation Evaluation 1 A None 2.2E−05 D A D D 2 A None9.5E−04 D A D D 3 C D Unchanged 3.6E+00 B A A B 4 C D 2.4E+01 A A A A 5C D 1.5E+01 A A A A 6 C D 5.0E+01 A A A A 7 C D 3.6E+01 A A A A 8 C D4.3E+00 B B A B 9 A, E None 1.0E−06 D D D D 10 A, E None 1.0E−06 D D D D11 C A, D 7.0 4.5E−01 B A B B 12 C A, D 9.2 1.2E+00 B A B B 13 C A, D15.0  6.4E−01 B A B B 14 C D Unchanged Unchanged B A B B 15 C DUnchanged Unchanged A A A A 16 F G Unchanged 2.4E+01 A A A A 17 F G2.2E+01 A A A A 18 F G 6.4E−01 B A B B 19 F G 6.4E−01 B A B B 20 NotJoined D 21 C D Unchanged 1.8E+01 A A A A 22 C D 1.5E+01 A A A A 23 C D1.6E+01 A A A A ¹⁾A: Fe₂O₃, B: Fe₃O₄, C: (Fe, Ni)₂O₃, D: (Fe, Ni)₃O₄, E:Fe₂NiO₄, F: (Fe, M)₂O₃, G: (Fe, M)₃O₄ (M is any one of Cu, Zn, Mn, andCo) ²⁾Unmeasurable 3) E+01 represents 10¹ and E−01 represents 10⁻¹

Next, the formation of the electrode on the honeycomb structural bodywas investigated. As for the formation of the electrode, a thermalspraying method and a printing method were investigated. In thisinvestigation, Experimental Examples 26 to 36 and 39 to 45 correspond toexamples of the present invention, and Experimental Examples 24, 25, 37,and 38 correspond to comparative examples.

Experimental Examples 24 to 36

An electrode containing a Fe₃O₄ phase was formed on a honeycombstructural body by thermal spraying. As a thermal spraying raw material,Fe₂O₃ and NiO were fired in the air at 1,200° C. and pulverized into apowder by a ball mill, and the powder thus obtained was granulated tohave a D90 of 197.8 μm, a D50 of 83.3 pin, and a D10 of 9.3 μm. As asubstrate to be sprayed, a Si-bonded SiC-made honeycomb was used, and onan outer wall thereof, plasma spraying was performed in an airatmosphere under the conditions shown in Table 3. In this case, anelectrode having a length of 65 mm, a width of 15 cm, and a thickness tof 12 to 25 μm was formed by thermal spraying on a Si-bonded SiC-madehoneycomb having a diameter of 90 mm and a length L of 75 mm. InExperimental Examples 25 to 36, L1/L was 0.87, and X1/X was 0.053. Inaddition, in Experimental Example 24, no electrode was formed withoutperforming thermal spraying, and for example, the electrical resistanceof the partition wall of the outer circumference was measured.

TABLE 3 Thermal Spraying Raw Material Crystal Experi- Thermal SprayingCondition Phase of Particle Size mental Gas Introduced Cur- Volt- RawRaw Material Component of Distribution Exam- Material of L/min rent ageMaterial Spraying Raw Material mass % <10 ples¹⁾ Substrate Ar H₂ A VPowder Fe₂O₃ TiO₂ NiO CuO ZnO Mn₃O₄ CoO Total μm D50 24 Si-bonded NoneSiC 25 Si-bonded 41 14 600 72 Fe₂O₃ 100 100 9.5 80 SiC 26 Si-bonded 41 0889 38 (Fe, Ni)₂O₃ 95.3 4.7 100 9.8 85 SiC 27 Si-bonded 41 4 600 59 (Fe,Ni)₂O₃ 95.3 4.7 100 9.8 85 SiC 28 Si-bonded 41 14 600 72 (Fe, Ni)₂O₃95.3 4.7 100 9.8 85 SiC 29 Si-bonded 41 14 600 72 (Fe, Ni)₂O₃ 98.6 1.4100 9.5 75 SiC 30 Si-bonded 41 14 600 72 (Fe, Ni)₂O₃ 90.6 9.4 100 8.5 70SiC 31 Si-bonded 41 14 600 72 Fe₂O₃, 95.3 4.7 100 6.5 60 SiC NiO 32Si-bonded 41 14 600 72 Fe₂O₃, 97.6 1.0 1.4 100 8.5 70 SiC TiO₂, NiO 33Si-bonded 41 14 600 72 Fe₂O₃, 98.6 1.4 100 8.5 70 SiC CuO 34 Si-bonded41 14 600 72 Fe₂O₃, 98.6 1.4 100 8.5 70 SiC ZnO 35 Si-bonded 41 14 60072 Fe₂O₃, 98.6 1.4 100 8.5 70 SiC Mn₃O₄ 36 Si-bonded 41 14 600 72 Fe₂O₃,98.6 1.4 100 8.5 70 SiC CoO ¹⁾Examples in which electrode was formed bythermal spraying

Experimental Examples 37 to 45

An electrode containing a Fe₃O₄ phase was formed on a honeycombstructural body by printing. As a printing paste, a mixture formed byusing a Fe metal powder, NiO, a polyvinyl butyral) (PVB), and terpineolwas used. This paste was printed to have a shape of 65 mm×15 mm×0.2 mm(thickness t) on a Si-bonded SiC-made honeycomb having a diameter of 90mm and a length L of 75 mm. After drying was performed in the air at 80°C. for 1 hour, firing was performed in Ar at 750° C. The outline of theformation is shown in Table 4. In Experimental Examples 37 to 45, L1/Lwas 0.87, and X1/X was 0.053.

TABLE 4 Experi- Firing mental Firing Temper- Exam- Material of RawMaterial/mass % Atmo- ature ples¹⁾ Substrate Fe NiO TiO₂ Ni Total sphere° C. 37 Si-bonded 100.0 100 Ar 750 SiC 38 Si-bonded 98.9 1.1 100 Air 750SiC 39 Si-bonded 99.5 0.5 100 Ar 750 SiC 40 Si-bonded 99.5 0.5 100 Air750 SiC 41 Si-bonded 98.0 2 100 Air 750 SiC 42 Si-bonded 93.4 6.6 100Air 750 SiC 43 Si-bonded 87.1 12.9 100 Air 750 SiC 44 Si-bonded 97.0 1.91.1 100 Air 750 SiC 45 Si-bonded 98.2 1.8 100 Air 750 SiC ¹⁾Examples inwhich elextrode was formed by printing

(Measurement of Electrical Resistance)

In Experimental Examples 24 to 45 in which the electrode was formed bythermal spraying or printing, after a hole having a diameter of 2 mm wasformed in a part of a substrate having a size of 20 mm×20 mm, Ag wasbaked as the electrode, and the electrical resistance of an electrodematerial (oxide ceramic containing a Fe₃O₄ phase) was measured by atwo-terminal method. In addition, the electrical resistance of thehoneycomb structural body was also measured. For the electricalresistance measurement of the honeycomb structural body, Al foil waspushed to an outer wall of the honeycomb or the electrode portion, andmeasurement was performed by a two-terminal method.

(Heat Resistance Test)

The heat resistance test was performed on the samples of ExperimentalExamples 24 to 45. In the heat resistance test, each sample was left inthe air at 850° C. for 24 hours. After the heat resistance test, forexample, the electrical resistance was measured.

(Measurement of Heat Generation Distribution of Honeycomb StructuralBody)

After Al foil was pushed to an outer wall of a honeycomb having adiameter of 90 mm and a length L of 75 mm or the electrode portion, anelectricity of 2.25 kW was supplied for 25 seconds, and the heatgeneration distribution was measured by a thermography camera.

(Results and Discussion)

The measurement results of Experimental Examples 24 to 36 arecollectively shown in Table 5, and the measurement results ofExperimental Examples 37 to 45 are collectively shown in Table 6. InExperimental Example 24, although the honeycomb structural body wasprovided with no electrode, the change in electrical resistance beforeand after the heat resistance test was not observed. On the other hand,in Experimental Example 24, both before and after the heat resistancetest, irregularities were generated in the heat generation distribution.In Experimental Example 25, an electrode of a Fe₃O₄ phase in which Niwas not solid-dissolved was formed. It was found that in ExperimentalExample 25, although the electrode was provided, the heat resistance wasinferior. In this Experimental Example 25, although no irregularitieswere generated in heat generation distribution before the heatresistance test, after the heat resistance test, the electricalresistance was increased, and irregularities were also generated in theheat generation distribution. That is, it is believed that the oxidationresistance was still not sufficient. On the other hand, in ExperimentalExamples 26 to 36, before and after the heat resistance test, the changein electrical resistance was not observed, and irregularities were notgenerated in the heat generation distribution. In Experimental Examples26 and 27 in which the thermal spraying conditions, such as the mixinggas ratio and the plasma energy, were changed, results similar to eachother could be obtained. In Experimental Examples 28 to 30 in which thecomposition range of the electrode was changed, it was found thatpreferable results could be obtained. Furthermore, in ExperimentalExamples 31 and 32 in which the thermal spraying raw material waschanged, results similar to each other could also be obtained.Furthermore, in Experimental Examples 33 to 36 in which the solutecomponent was changed, results similar to each other could also beobtained.

TABLE 5 Electrical Resistance Change in Local Heat Generation ofElectrode Material Electrical in Honeycomb Before After ResistanceStructural Body Amount Heat Heat Electrical of Honeycomb Before AfterExperi- Electrode After Thermal Spraying of Peak Resis- Resis-Resistance Structural Body Heat Heat mental Thick- Shift of tance tanceof Honeycomb After Heat Resis- Resis- Exam- ness Width Length ElectrodeTest Test Structural Resistance tance tance ples¹⁾ Material μm mm mm °Ωcm Ωcm Body/Ω Test/Ω²⁾ Test Test 24 None 9.0E+01 A Present Present 25Fe₃O₄ 20 15 65 None 6.2E−01 1.1E+03 7.2E+01 B None Present 26 (Fe,Ni)₃O₄ 12 15 65 0.101 4.0E−02 4.2E−02 6.0E+01 A None None 27 (Fe, Ni)₃O₄18 15 65 0.101 4.0E−02 4.2E−02 6.2E+01 A None None 28 (Fe, Ni)₃O₄ 23 1565 0.101 3.0E−01 2.8E−01 6.5E+01 A None None 29 (Fe, Ni)₃O₄ 20 15 650.06 4.0E−02 4.2E−02 6.1E+01 A None None 30 (Fe, Ni)₃O₄ 25 15 65 0.20323.0E−02 2.8E−02 6.5E+01 A None None 31 (Fe, Ni)₃O₄ 25 15 65 0.1016.8E−02 6.5E−02 6.2E+01 A None None 32 (Fe, Ti, Ni)₃O₄ 20 15 65 0.1414.0E−02 4.2E−02 6.0E+01 A None None 33 (Fe, Cu)₃O₄ 22 15 65 0.0313.8E−02 4.2E−02 6.0E+01 A None None 34 (Fe, Zn)₃O₄ 22 15 65 0.0283.6E−02 4.5E−02 6.1E+01 A None None 35 (Fe, Mn)₃O₄ 21 15 65 0.0214.5E−02 1.6E+00 6.1E+01 A None None 36 (Fe, Co)₃O₄ 23 15 65 0.0224.2E−02 1.6E+00 6.0E+01 A None None ¹⁾Examples in which electrode wasformed by thermal spraying ²⁾A: Change by 1 digit Ω or less, B: changeby 2 digits or more 3) E+01 represents 10¹ and E−01 represents 10⁻¹

As shown in Table 6, in Experimental Examples 37 and 38 in which theelectrode was formed by a printing method, although the electrode wasprovided, after the heat resistance test, the electrical resistance wasincreased, and irregularities were also generated in the heat generationdistribution; hence, it is believed that the heat resistance was stillnot sufficient. On the other hand, in Experimental Examples 39 to 45,before and after the heat resistance test, the change in electricalresistance was not observed, and no irregularities were generated in theheat generation distribution. Incidentally, in Experimental Example 39,an electrode firing atmosphere was changed; in Experimental Examples 40to 43, the composition range of Ni of the electrode material waschanged; in Experimental Example 44, Ti was added besides Ni; and inExperimental Example 45, the raw material was changed.

TABLE 6 Electrical Resistance Change in Local Heat Generation ofElectrode Material Electrical in Honeycomb Before After ResistanceStructural Body Heat Heat Electrical of Honeycomb Before After Experi-Electrode Resis- Resis- Resistance Structural Body Heat Heat mentalThick- tance tance of Honeycomb After Heat Resis- Resis- Exam- nessWidth Length Test Test Structural Resistance tance tance ples¹⁾ Materialμm mm mm Ωcm Ωcm Body/Ω Test/Ω²⁾ Test Test 37 Fe₃O₄ 160 15 65 6.2E−014.6E+04 7.1E+01 B None Present 38 Fe₂O₃, Fe₃O₄, TiO₂ 220 15 65 2.0E+001.1E+03 7.9E+01 B None Present 39 (Fe, Ni)₃O₄ 150 15 65 4.0E−02 4.0E−026.0E+01 A None None 40 (Fe, Ni)₃O₄ 220 15 65 3.3E−01 3.6E−01 6.1E+01 ANone None 41 (Fe, Ni)₃O₄ 210 15 65 6.8E−02 6.5E−02 6.1E+01 A None None42 (Fe, Ni)₃O₄ 230 15 65 1.8E−02 2.0E−02 6.0E+01 A None None 43 (Fe,Ni)₃O₄ 220 15 65 3.0E−02 2.8E−02 6.1E+01 A None None 44 (Fe, Ni, Ti)₃O₄210 15 65 4.0E−02 4.0E−02 6.2E+01 A None None 45 (Fe, Ni)₃O₄ 220 15 652.6E+01 2.6E+01 6.0E+01 A None None ¹⁾Examples in which electrode wasformed by printing ²⁾A: Change by 1 digit Ω or less, B: change by 2digits or more 3) E+01 represents 10¹ and E−01 represents 10⁻¹

It was found that in an electrode formed of an oxide ceramic containinga Fe₃O₄ phase in which a solute component was solid-dissolved, when theelectrode size was 15 mm×65 mm, the thermal stability and the oxidationresistance were further improved, and the heat generation distributioncould be made more uniform.

It is to be naturally understood that the present invention is notlimited at all to the examples described above and may by performed invarious modes without departing from the technical scope of the presentinvention.

What is claimed is:
 1. A honeycomb structural body comprising: apartition wall formed of a porous ceramic which forms and defines aplurality of cells each functioning as a flow path of a fluid andextending from one end surface to the other end surface; and an outercircumference wall formed along the outermost circumference, wherein anoxide ceramic containing a Fe₃O₄ phase in which a solute componentcapable of forming a spinel-type oxide with Fe is solid-dissolved isformed.
 2. The honeycomb structural body according to claim 1, whereinthe oxide ceramic is an electrode formed on an outer surface of thehoneycomb structural body.
 3. The honeycomb structural body according toclaim 1, wherein the oxide ceramic is an electrode and formed on anouter surface of the honeycomb structural body so that the ratio of alength L1 of the electrode to a total length L of the honeycombstructural body in the flow path direction is in a range of 0.1 to 1 andthe ratio of a length X1 of the electrode to an outer circumferencelength X of the surface of the honeycomb structural body perpendicularto the flow path is in a range of 0.02 to 0.3.
 4. A honeycomb structuralbody comprising: a partition wall formed of a porous ceramic which formsand defines a plurality of cells each functioning as a flow path of afluid and extending from one end surface to the other end surface; andan outer circumference wall formed along the outermost circumference,wherein an electrode formed of an oxide ceramic containing a Fe₃O₄ phasein which a solute component capable of forming a spinel-type oxide withFe is solid-dissolved is formed on an outer surface of the honeycombstructural body so that the ratio of a length L1 of the electrode to atotal length L of the honeycomb structural body in the flow pathdirection is in a range of 0.1 to 1 and the ratio of a length X1 of theelectrode to an outer circumference length X of the surface of thehoneycomb structural body perpendicular to the flow path is in a rangeof 0.02 to 0.3.
 5. The honeycomb structural body according to claim 3,wherein the oxide ceramic is formed so that the ratio of the length L1to the total length L is in a range of 0.8 to
 1. 6. The honeycombstructural body according to claim 3, wherein the oxide ceramic isformed so that the ratio of the length X1 to the outer circumferencelength X of the surface is in a range of 0.05 to 0.3.
 7. The honeycombstructural body according to claim 3, wherein the electrode is formed sothat the ratio of an area S1 of the electrode to a total side surfacearea S of the outer surface of the honeycomb structural body is in arange of 0.002 to 0.3.
 8. The honeycomb structural body according toclaim 1, wherein oxide ceramic contains at least one of Mn, Co, Ni, Cu,and Zn as the solute component.
 9. The honeycomb structural bodyaccording to claim 1, wherein the oxide ceramic contains the solutecomponent in a range of 0.5 to 30 percent by mass.
 10. The honeycombstructural body according to claim 1, wherein the oxide ceramic containsNi as the solute component, and the peak shift of the (751) plane ofFe₃O₄ measured by x-ray diffraction using the CuKα line is 0.02° ormore.
 11. The honeycomb structural body according to claim 1, whereinthe oxide ceramic contains Fe as a first component and at least one ofSi, Zr, Ti, Sn, Nb, Sb, and Ta as a second component.
 12. The honeycombstructural body according to claim 1, wherein the oxide ceramic has anelectrical conductivity of 1×10⁻¹ (S/cm) or more.
 13. The honeycombstructural body according to claim 1, wherein the partition wall isformed of a Si-bonded SiC material.
 14. A method for manufacturing ahoneycomb structural body comprising: a partition wall formed of aporous ceramic which forms and defines a plurality of cells eachfunctioning as a flow path of a fluid and extending from one end surfaceto the other end surface; and an outer circumference wall formed alongthe outermost circumference, the method comprising: a forming step of,by using a raw material powder including a Fe raw material powder whichcontains at least one of a Fe metal powder and a Fe oxide powder and asolute component powder which contains a solute component capable offorming a spinel-type oxide with Fe, forming an oxide ceramic layercontaining a Fe₃O₄ phase in which the solute component issolid-dissolved for the honeycomb structural body.
 15. The method formanufacturing a honeycomb structural body according to claim 14, whereinthe forming step includes a thermal spraying step of melting and thermalspraying the raw material powder.
 16. The method for manufacturing ahoneycomb structural body according to claim 14, wherein the formingstep includes a firing step of forming the raw material powder in thehoneycomb structural body and then firing the raw material powder. 17.The method for manufacturing a honeycomb structural body according toclaim 14, wherein in the forming step, the raw material powder is meltedand thermal sprayed to form a joint portion of the oxide ceramic whichjoins an electrode functioning as a first member formed on an outersurface of the honeycomb structural body and a terminal functioning as asecond member adjacent to the electrode.